PROCEEDINGS OF THIRTY-SIXTH FRUIT-GROWERS [ CONVENTION. 127 



but are in evidence, in numbers, late into October. These second brood 

 larva? are much more numerous than those of the first generation, and 

 cause the most damage. The great majority of the second generation 

 worms have the wintering-over instinct and so do not develop into 

 moths until the following spring. A summer generation requires about 

 sixty-five days, so there is a possibility of a third brood in October. 



Sprays applied during the winter and contact insecticides in the 

 summer are of little or no value in the control of the codling moth. 

 Poisoning with arsenic has on the other hand proved very effective when 

 the spraying is done at the proper times. The compound of arsenic 

 should be sufficiently insoluble to enable its free use without danger of 

 foliage injury, and the applications must be made just before the most 

 important hatches of the worms. Numerous compounds of arsenic have 

 been proposed, but at present arsenate of lead meets all requirements 

 best. 



Some confusion has arisen from the fact that there are two theories 

 of spraying and two kinds of arsenate of lead. The two lead com- 

 pounds are known as pyro and ortho arsenates. The pyro arsenate con- 

 tains a greater amount of arsenic than the ortho compound, and so is 

 a more active poison. It also releases some arsenic to water solution, 

 rendering use in the coast climates dangerous. The ortho compound, 

 on the other hand, is safe under these conditions. 



The two theories of spraying have likewise originated under opposite 

 climatic conditions. In the dry interior it has been demonstrated that 

 the calyx cup spraying is most important, and may even be so effective 

 as to render further applications unnecessary. But in the rain belt of 

 the Pacific coast and also in many other sections of the country, the 

 relative value of the calyx cup application is not nearly so great. In 

 California coast districts applications for both broods must be made, 

 and will include three or four sprayings, according to the abundance 

 of the codling moth. 



The other caterpillars mentioned in the list of apple insects are nor- 

 mally leaf feeders, appearing in the early spring and coming to ma- 

 turity before the middle of June. April and May are the months of 

 caterpillars. Many caterpillars have but one generation a year, and 

 this is true of tent caterpillars, tussock caterpillars, and cankerworms. 

 The tent and tussock caterpillars pass the winter in the egg stage. 

 These eggs are deposited on the trees by the moths in June and July, 

 but do not hatch until the following spring. The female moths of the 

 tussock caterpillars are wingless, so distribution is effected by the 

 migration of the larva? and the accidental transportation of eggs and 

 young caterpillars. Two species of cankerworms are present, called 

 fall and spring cankerworms. Like the tussock caterpillar, the female 

 moths are wingless, but the eggs are not laid in the early summer. One 

 species deposits late in the fall while the other waits until the early 

 spring. The adult larval and pupal stages are passed in the ground 

 under the trees, so the wingless females are obliged to ascend the trunks 

 in order to lay their eggs. 



The tent caterpillars and cankerworms injure the trees by defolia- 

 tion, and must be quite numerous before serious damage is done. Com- 

 plete defoliation by caterpillars destroys the crop for two years. The 

 tent caterpillars spin a web protection capable of covering the whole 



